The proposed research consists of projects designed to characterize the nature and function of Fc receptors for IgE on lymphocytes and monocytes/alveolar macrophages. 1. Lymphocytes from normal donors and atopic patients will be cultured in vitro in presence of aggregated IgE and analyzed for changes in expression of Fc receptors for IgE, IgG and IgM. 2. Lymphocytes from normal donors and atopic patients will be depleted or enriched for cells with Fc receptors for IgE. These cells will then be cultured in vitro and the supernatants analyzed for IgE by a radioimmunoassay. 3. Peripheral blood monocytes and alveolar macrophages will be analyzed for their ability to form specific specific IgE rosettes and cellular cytotoxicity towards IgE coated target cells. 4. The ontogeny of rat lymphocytes with Fc IgE receptors will be determined in low and high IgE responder rat strains. The effect of a rat IgE myeloma tumor on the percentages of Fc IgE receptor positive lymphocytes and macrophages will also be investigated.